Heart Matters

BY NICK ZAGORSKI

On Valentine’s Day, people’s thoughts naturally turn to hearts, though typically of the chocolate or candy variety. However, this holiday should also serve as a reminder of the importance of the human heart, quietly beating more than 100,000 times and pumping almost 2,000 gallons of blood not just this day, but every day of the year. Unfortunately, unlike love, the heart is not everlasting; recent statistics suggest that this year, more than 1 million people in the U.S will experience a new or recurrent heart attack, more than 400,000 will die from coronary heart disease and bad hearts will total some $300 billion in direct and indirect costs.

However, with increased understanding of how the heart works, these numbers can surely improve. So, in honor of this special heart-related holiday, the American Society for Biochemistry and Molecular Biology is highlighting some of our members who devote their time to heart-related research, looking to make heart defects, disease and failure a thing of the past.

Kenneth Walsh

Director, Whitaker Cardiovascular Institute, Boston University School of Medicine

Kenneth Walsh took over as the third director of Boston’s Whitaker Cardiovascular Institute in February 2008 and is looking to enhance translational research efforts.

In the arena of cardiovascular research, most scientists fall into one of two camps: those who study the “cardio” and those who study the “vascular.” Not many have focused their efforts on the interplay of the two, which Kenneth Walsh finds somewhat unusual.

“In the body, these two systems, heart muscle and blood vessels, are talking to each other all the time,” he says, “whether it’s in response to physiological stimuli like exercise, in response to some injury or during normal growth, so the heart and vasculature can keep pace with the rest of the body.”

The mechanisms behind this inter-tissue communication are the major theme underlying Walsh’s lab at Boston University. His methods involve a two-pronged approach, first identifying critical proteins or pathways through bioinformatics (as Walsh says, “mining the cardiac secretome”), then validating uncovered molecules using genetic models.

In several instances, the new molecules have proved to be potential biomarkers for pathological conditions, such as in Walsh’s recent work identifying follistatin-like 1 as a factor that may determine the susceptibility of the heart to ischemic injury.

And, Walsh is definitely interested in pursuing diagnostic or therapeutic avenues, because, as he says, “I don’t just want to cure heart disease in mice.”

Another area Walsh’s group currently is exploring— and another overlooked field, in his view— is how metabolic dysfunction, especially associated with obesity and diabetes, affects the heart’s activity. As Walsh notes, obese individuals have hearts that are larger than the predicted body-heart size ratio, causing hypertension and other problems.

“It’s a big driver of cardiovascular disease, yet, at cardiovascular meetings, you really won’t see a lot of metabolic talks,” Walsh says. “It’s starting to catch on, but, considering the clinical significance of the problem, it’s still vastly underrepresented.”

That’s why Walsh has made the metabolic-cardiovascular connection an initiative not just in his group, where’s he’s studying the role of the adipose-derived cytokine adiponectin in inflammation and heart disease, but also at the Whitaker Cardiovascular Institute, which he currently directs.

“It’s a very collaborative environment, with a tremendous amount of expertise, and we’re still growing,” Walsh says proudly of the institute. “And being located in the heart of Boston, one of the best places to do biomedical research, is rewarding as well.”

“I think the only drawback right now is that my duties keep me away from the lab often, and I like working with my hands,” he continues. “But I think my lab is better served when I am working in my office.”

In looking back, though, Walsh sometimes wonders how he reached this point. After all, 30 years ago, he was just a young and headstrong biochemistry student working under Daniel Koshland without much knowledge or interest in cardiovascular research.

Then, when he received his first faculty appointment in the physiology department at Case Western Reserve University, he was surrounded by colleagues who worked in the cardiovascular field, so he started going with the flow, in a manner of speaking.

As for taking on a leadership role, Walsh notes: “I guess I’ve always been good at two things: chemistry and getting people to work together.”

Eric N. Olson

Professor and chairman of the department of molecular biology, University of Texas Southwestern Medical Center

Eric N. Olson and Willie Nelson. The iconic singer/songwriter and his wife, Annie, established a professorship to support Olson’s work on cardiac stem cells.

It’s appropriate that one of Eric N. Olson’s favorite tunes to play with his rock band, the Transactivators (in which Olson plays guitar and harmonica), is Neil Young’s “Heart of Gold.” While each organ in the human body is a complex, fascinating and, in most cases, essential physiological machine, in Olson’s view, any discussions as to which organ should be considered the most vital begins and ends with the heart.

“The heart is incredibly unique,” he says. “It performs nonstop rhythmic contractions every second, and it’s a wonderful model for understanding how genes are coordinately regulated and control organ formation. Plus, adult cardiac cells never divide, making them an ideal system to study the cell cycle.”

“Oh, and of course, unlike some other organs, the heart lacks an intrinsic mechanism to repair itself,” he adds. “So, cardiovascular disease still remains the No. 1 killer in the United States, while congenital heart defects are the most common birth defects seen in humans: They occur in about 1 percent of all live births.”

It’s the latter statistic that has been a driving force for Olson’s research at UT-Southwestern; since arriving in 1995 from the M.D. Anderson Cancer Center, his group has been hard at work identifying the genes and transcription factors responsible for forming the heart in developing embryos and analyzing how defects in those genetic networks lead to congenital heart disease.

The work has been a natural progression from Olson’s earlier— and continuing— studies into skeletal and smooth muscle differentiation, through which he discovered several transcription factors involved in that process and realized many of them had similar roles in cardiac muscle.

Olson combines genetic and biochemical approaches to discover novel cardiac transcription factors, including mutational studies in Drosophila, which has turned out to be an excellent model organism for studying heart defects. “It may not seem readily apparent, but many key muscle transcription factors were first discovered in fruit flies,” he says, noting that the fruit fly heart, a simplistic linear pump, closely resembles the heart tube in early mammalian embryos.

Olson notes that his field has been quite dynamic recently (due in no small part to his efforts, which include the discovery of the transcription cofactor myocardin and the identification of both calcineurin and histone deacetylases as regulators of cardiac hypertrophy). “We’ve made some dramatic progress this past decade,” he says. “We’ve gone from knowing virtually nothing about the molecular blueprint for heart development to knowing most of the regulators involved, though we still need to tease out how they all fit together.”

A new wrinkle in that blueprint, and one that’s been a significant focus of Olson’s work the past few years, is the emerging role of microRNAs in heart development and disease. From identifying the importance of miR-126 in vascular integrity to miR-133’s role in cardiomyocyte proliferation, “we’ve managed to uncover a treasure trove of new regulators that affect virtually every process associated with heart disease,” he says, “such as fibrosis, hypertrophy and atrophy and blood vessel formation.”

Combining the potential power of RNA silencing with existing technologies for delivering therapeutics to the heart, Olson is preparing to take these microRNA discoveries to the treatment stage; he even started up a biotech company, called miRagen Therapeutics, to help him with this process.

Journal of Biological Chemistry research highlight: Down Syndrome Critical Region-1 Is a Transcriptional Target of Nuclear Factor of Activated T Cells-c1 within the Endocardium during Heart Development. JBC 282, 30763-30679.

Daria Mochly-Rosen

Professor of chemical and systems biology, Stanford School of Medicine

Daria Mochly-Rosen was introduced to protein kinase C through her postdoctoral mentor, Daniel Koshland, and has since been instrumental in uncovering this enzyme’s role in heart function.

In an unusual twist, a run-of-the-mill lecture at a conference became the catalyst for Daria Mochly-Rosen’s foray into an exciting new line of research.

In the mid-1990s, Mochly-Rosen showed that different isozymes of protein kinase C were located in discrete subcellular regions of cardiac muscle cells and that shutting off individual isozymes with peptides could make the cells beat faster or slower. This finding confirmed her hypothesis that PKC isozymes have unique localizations in all cells, mediated by binding to isozyme-specific anchoring proteins known as receptors for activated C-kinase, or RACKs.

The identification of RACKs helped explain the mystery of how the many similar-appearing forms of PKC could mediate a range of processes in diverse— and, in the case of heart muscle, even opposite— ways.

“However, when I presented these results at an American Heart Association conference, I noticed a lot of uninterested scientists in the audience,” she says. Afterwards her colleague Joel Karliner of the University of California, San Francisco, informed her that cardiologists didn’t really care about heart rate, because they had perfectly good ways of managing it.

“So I asked him what cardiologists did care about, and he told me heart attacks,” Mochly-Rosen says. However, she was hardly familiar with this area. (A biochemist by training, she had primarily worked with heart cells because their beating was an easy phenotype to observe.) “But then Joel told me not to worry— he would ask one of his cardiology fellows, Mary Gray, to join my lab.”

Since then, Mochly-Rosen always has had at least one physician in her lab at Stanford University to help with her research into PKCs role in heart function, and her group has uncovered a lot of valuable information, including the fact that either activation of epsilon PKC or inhibition of delta PKC can protect the heart from ischemia damage. In fact, one of the delta PKC inhibitor peptides she used in her earlier heart rate studies (delta V1-1) is now in phase II clinical trials for heart attack treatment.

“The people at the AHA conferences are a bit more attentive when I speak now,” she jokes.

In the past couple of years, Mochly-Rosen has turned her attention to one of the proteins activated by PKC; through a proteomic approach aimed at understanding how epsilon PKC is heart-protective, she identified aldehyde dehydrogenase 2 as an epsilon PKC target. She then confirmed a causal relationship between epsilon PKC and ALDH2 (alcohol dehydrogenase) by developing a small molecule activator of ALDH2 and showing that this activator produced the same cardioprotective effects in rat models as epsilon PKC activation.

Mochly-Rosen and her lab are now looking at exactly why PKC turns on ALDH2 to protect the heart. However, the importance of ALDH may be the key to the complex role of alcohol in relation to the heart, as alcohol consumption has been linked to both beneficial and damaging cardiac effects.

At the least, this new revelation gives Mochly-Rosen her own change in perspective. “I always thought ALDH was a boring enzyme; it was always active and seemed to have a simple function,” she says. “But now I know better.”

Mark A. Sussman

Professor of biology, San Diego State University

In 2006, Mark A. Sussman helped facilitate a National Institutes of Health program project grant for San Diego State University and the University of California, San Diego. It was the first such award for any school in the 23-campus California State University system.

When Mark A. Sussman completed his doctoral studies at the University of Southern California, he asked one of his thesis committee members on what area of science his postdoctoral fellowship should focus. “He told me to do something completely different than my graduate school research, because my postdoc was my last opportunity to be stupid, scientifically speaking.”

So, Sussman put his dissertation on viral immunology on the bookshelf and pursued his interests in the cytoskeleton, first with Velia Fowler at The Scripps Research Institute and then with Laurence Kedes back at USC. He began working on the actin-capping protein tropomodulin and found that the structural protein was expressed in specific subcellular locations in heart muscle, and, when it was over-expressed, it would prevent proper heart contraction and eventually led to heart failure as the organ tried unsuccessfully to remodel.

In the ricocheting world of science, that discovery soon led to a cardiovascular research fellowship, which, in turn, led to Sussman’s development of the first mouse model of dilated cardiomyopathy and a long and fruitful career studying heart failure.

However, when the California native returned home to take up a position at San Diego State University, he decided a change of pace was in order. “I had sort of become an expert in making mouse hearts that failed, and I now wanted to see what I could do to keep a heart working properly,” he says.

Sussman became intrigued with Akt/PKB kinase, a signaling protein that either helped protect heart cells or caused it to fail, depending who you asked. “It was a big paradox,” he says. “Researchers found that if you activated Akt in heart cells, by adding agents like insulin like growth factor to the media, it made the cells resistant to death. But, when they induced Akt in mice by genetic manipulation, the heart responded by remodeling and eventually failed.”

The reason for the paradox, as Sussman discovered, was that Akt goes through a specific set of localizations when activated and has specific targets, depending on where it is; in the case of cardioprotective stimulators, Akt ended up in the nucleus.

“So it’s not just activity level but where the activity occurs,” he says. “Thus, the brute-force approach of simply inducing Akt in the heart was like drinking water from a fire hose: You’ll quench your thirst, but a lot of bad stuff is going to happen as well.” Once Sussman mimicked the process seen in cell culture and localized Akt to the nucleus, the mice exhibited the expected damage-resistant hearts.

Those studies did present one mystery, though. Many of the important cardioprotective targets where in the cytoplasm; so how did Akt turn them on while trapped in the nucleus? The answer was that Akt turned on another activator protein called PIM-1, which mediates the protective effects.

And PIM-1, Sussman believes, is a key piece for regenerative medicine and stem-cell therapies for the heart. Early work in repairing hearts with stem cells was unsuccessful, because the stem cells did not graft well and died off; but combining stem cells with activation of PIM-1 and the survival pathway might make it work. Just recently, he had success in mouse models, and now he’s hoping for similar results using human cells in immunized mice and then large-animal models.

And if all goes as planned, Sussman thinks we might soon see a future of genetically rebuilding hearts after acute stress or chronic injury. “We’ll put the surgeons out of business, and I can spend my days on the beach, drinking cocktails with little umbrellas in them.”